Mixing circuit arrangement



A. VAN WEEL MIXING CIRCUIT ARRANGEMENT Aug. 5, 1952' IINVENTOR. V ADELBERT VAN WEEL Filed Sept. 10, 1946 Patented Aug. 5, 1952 MDHNG CIRCUIT ARRANGEMENT Adelbert'van Weel, Eindhoven,Netherlands, assignor to Hartford National .BankUandHTrust: Company,'Hartford, (301111., as trustee Applicationzseptemb'er 10, 1946, Scrial No. 695;889 Inithe Netherlands October 21,1943:

Section 1; Public 'Law 690, Ai1gust'S,C19Y4B" Patenticxpires October 2 ,1 96? 7 9 Claims.

'My copending United States-patent application No. 680,930, filed July 2, 1946, PatentNo. 2,582, 726, granted January 1952, relates'to a mix-- ing circuit arrangement inwhich the incoming oscillations are supplied-in pushpull and the 10- cal 'oscillations'in phase coincidence'to the input electrodes of two discharge systems; and in which the circuit "constituted by the "parallel-connected impedances of both halves of the push-pull -circuit and the parallel connected input impedances; jointly with the impedances" common to temand in which are circulating currents -associated with this system and having the irequency of the local oscillations.

copending United States patentapplica tion aforementioned, describes a form o'f construction, in which the impedances common to the inputcircuitsi. e; 'the-impedances by means of which the said a circuit- -'(-herei-nafter= called single phaseci-rcui-t) is tuned to the-frequency of the local-' oscillation-s, are interposed between the middle of the push-pull circuit and ground, and between the interconnected cathodes of the discharge 'systemsand ground respectively; Due to this, only one of "the two sa idpoin ts the m-iddle of the push-pull circuit orthejunction of the cathodes of the discharge systems) can" be grounded. In a particular form of construction,

in which theimpedances common to the input circuits are distributedwith respect to the junctions of the antenna to thepush-pull circuit i-n order that the antenna may-be connected in a voltageminimum of the local oscillations, none of these p'oints ca-n begrounded.

The ob'iect of 'the present i'invention is to provide greaterfreedom in :groundingf'the junction of (the 'cathodes generally the junction oftwo corresponding input electrodes :of the dischargesystems and/or the middle of the push-pull cir-e' cuit;

According to the-invention this is achieved by tuning the single phase circuit :to'the frequency of "the-local oscillations :by means of .a network interposed sbetween the junction of the two cor=- v responding input "electrodes ofthe-discharge "sys-- tems and/or the' middle'of the "push-pull circuit" on the one-hand and the remaininginput e1ec= trodes "and/or'the antennajuncti'ons on-the'other 7 hand.

This 1 permits either the said junction or"the" middl'e of -"t'-he--push'- pull- *circuit or both points; to be connected at will to "a-point'ihaving a'con; sta-nt potential (ground) On'the 'otih'erhand; it is possible at the "sametime"to"'connect"tife' antenna in a- 'voltage "mini-mum of the "loca11fos= c iI-la'tionsand/or to match the "antennafconven iently-to the discharge-systems:

Grounding the said" points" or "any of themii yields various advantages:- Fcir instance, when the-cathodes of the discharge? systemsiare bo'th connected to ground'the cathode direct current and the heating current mayfbe "supplied to those systems without *any difiicultyor complication'in the construction. In the case" of" the -control-' grids l of the discharge systems being" interconnected and the-"middle of thepush-pull circuit disposed 5 between the cathodes "heing grounddi the two currentsmay also "besupplie'd'in a very; simple manner; By making useofi'a positive feedback for the singleephase circuit; the local. oscillations may be-jproduced in' the circuit '.ar'-l-' rangement itself. When this" method is Jam-.- p'loyed,'"and the pair of 'interconnectedinputelem trodes is grounded; the circuit,'in"receivingshort waves, can be established lay-means '"of a" cavity, resonator; Whenthe middle of *thepushepull circuit is grounded, the signals 'received'lbyithe antenna and having *a frequency corresponding, to the intermediate *frequencyjcannot *causema terial disturbances;

Preferably the network is completed first 3' fol j lowed by tuning the push-pull circuit to theirs quency i of the incoming oscillations." In some cases, however, the pus'h'apull circuit willbe tuned to the frequency of theincoming" oscillations; followed by interposition of thefimpedan'ceszlby' means of which the-sing1e=phase circuit tuned to the frequencyof thelocal oscillations: I By; providing-t these imp'edances'thetuning'of" thjej push-pull circuit is compromisedasaruleiiHow? evergthls can be reducedto-*aminimum' by giv I ing- 'these-impedances-a suitable-value? f Preferably one or more-=starconnections are" provided whose branches connected totheinput electrodes -that are "not interconnected and to th'elantenna junctions respectively are-made in ductive, whereas the other brancl'ies"are made; capacitative. I 3' In a special case, in-which-*the-lncoming*"osclllations are supplied through a Lecher system to the discharge systems and in which the pushpull circuit is tuned to the frequency of the incoming oscillation, such an impedance can be interposed between the input electrodes which are not connected so as to achieve optimum matching of the antenna to the discharge systems.

As an alternative, magnetically coupled inductances may be included in each half of the push-pull circuit between the antenna junctions and the discharge systems (preferably close to the said junctions).

Figure 1 of the drawing represents a, mixing circuit according to my copending patent application heretofore mentioned, in which the incoming oscillations are supplied in push-pull relationship and the local oscillations in phase incidence to the control grids of two discharge systems I, I"; this mixing circuit forms part of a superheterodyne receiver for short waves. The incoming oscillations received by a dipole antenna 2, 2 are fed to two conductors 3, 3 forming part of a Lecher system which, by means of a short-circuit bridge 4, is tuned to the frequency of the incoming oscillations. The antenna 2, 2" is so connected to the Lecher system 3, 3" as to match the antenna correctly to the mixing tubes. The Lecher system is connected to the control grids R, R" of the dischargesystems ,l', I, and the cathodes of the discharge systems are interconnected at S. The middle of the short-circuit bridge 4, which is the middle of the push-pull circuit, is represented by P, the junctions of the antenna to the Lecher system being represented by Q, Q. Advantageously the two triodes I, I may be housed in one tube and may have a cathode in common.

A resonant circuit tuned to the intermediate frequency and consisting of two inductances 6, 6 and two condensers 1, 'l is connected in push-pull arrangementto the anodes of the two triodes. In series with coils 6, 6 are connected high-frequency chokes 8", 8", which serve to prevent a transmission of the incoming high-frequency oscillations to the receiver stages next to the mixing stage.- The junction of coils 6 and 6 is connected to ground through a condenser 9,1Which constitutes practically a short-circuit in regard to intermediate-frequency oscillations, and, through a resistance ID to the positive terminal of a'source of anode potential (not represented). Furthermore coils-G'and 6" are inductively coupled with a second intermediatefrequency circuit which consists of a coil H and a condenser l2 and from which the output voltage ofthe circuit arrangement is taken. The junction of the condensers I and 1 is connected to the cathodes of the two triodes so as to obtain an eleotric'circuit having a low impedance. in regard to anode currents having the oscillator frequency.

The middle of the push-pull circuit P is connected, to ground through a condenser l3, and the junction of the. cathodes 3 is grounded through a variablecondenser l4 and an inductanee [5 which is coupled with a coil l6 included in the output circuit of a diagrammatically rep-1 resentedlocal oscillator 0. With the aid of the coil I5, the local oscillations are fed to the input circuit of-the triode by means of so-called"cathodeinjection so that the local oscillations are set up in phase coincidence at the control-grids of the two triodes.

The aforesaid circuit arrangement, as shown by Fig. 1, exhibits the drawback that the input impedances of the triodes, which are represented by the capacities 5', 5", particularly in receiving ultra-short waves, have only a small value, due to which the voltage having the oscillator frequency and appearing between the control-grid and the cathode of each of the tubes usually becomes too low. To supply as high as possible a voltage having an oscillator frequency to the control grids of the mixing triodes, my copending patent application heretofore mentioned proposes tuning the circuit constituted by the parallel-connected impedances of both halves of the push-pull circuit and the parallel-connected input impedances of the two discharge systems, jointly with the impedances common to the input circuits of the two systems, to the frequency of the local oscillations.

In the circuit arrangement represented in Fig. 1, this circuit is constituted by the series-connection of the condensers I3, [4, the coil IS, the parallelconnected capacities 5 and 5" and the parallel connected Lecher lines 3 and 3". In fact, the voltage set up across the capacities 5 and 5" and having the oscillator frequency, 1. e. the voltage set up between the control grid and cathode of each triode, is a maximum in the case of series-resonance in the saidcircuit. Hence, this circuit must be tuned to the oscillator-frequency. By tuning, the series-connection of the condenser 13 and the parallel-com nected parts of the Lecher line between the points P and Q and Q respectively, as well as the series-connection of the condenser I4, the inductance l5, the parallel-connected input capacities 5 and 5- and the parallel connected parts of the Lecher line between points R, Q and R, Q respectively to the oscillator-frequency, the radiation of the local oscillations from the antenna 2 2" can be reduced to a minimum. To achieve this the capacity of condensers I3 and 14 may be made variable and these elements may be adjusted in such a manner that the radiation of the local oscillations from the antenna is a minimum, whereas the voltage having the oscillator frequency and being set up between the control-grid and the cathode of each triode is a maximum.

Due to the aforesaid expedients for tuning the single-phase circuit, neither the middle of the push-pull circuit P nor the junction of the cathodes can be grounded.- The present invention provides means for grounding at will one or both of these points.

Figs. 2, 3' and 4 of the drawing represent three embodiments of the invention.

The circuit arrangement shown in Fig. 2 substantially corresponds to that represented in Fig. 1, but the condensers l3 and M, the inductances l5 and I6 and the local oscillator O are missing. Furthermore, an inductance 22 is interposed between the junction of the cathodes S and the junction of the condensers 1 and 1''. Owing to the presence of this coil, through which flows exclusively a current having the frequency of the local oscillations, a positive feedback is obtained with respect to local oscillations. Assuming that the oscillator 0 were still available, an alternating anode voltage having the oscillator-frequency would be set up, due to the voltage loss through this coil, between the anode and cathode of each triode I and I". This voltage would lag the alternating control grid voltage by Consequently, currents having the oscillator-frequency, which are in phase with the alternating control-grid voltagean'd-which bring about undamping of thesingle-phase circuit; .are flowing-.1 through the anode/control-grid capaciities denoted by.2 l'. and 2|" in the drawing. In the .case under view'this undamping visraised to 'sucha degree that the arrangement itself generates oscillations having the oscillator frequency, so that a .separateoscillator can be dis-. pensed. with. V

According to the invention, a network, by means. of whichthe single-phase. circuit can be tuned to the frequency of the local oscillations, is interposed between the points P and, S ,on-the one hand and the points Q, Q" and R'x. R'." on theother,hand. Onehalf of this network consists-oi two equal inductances 11 and l I which aremplac'edun series-connection between the points Q. and Q", a-variable condenser [8 connected between the. point P and the junction of coils l1 and H:'-, and. the parts of the Lecher system 3', 3" located between the point? and the-points .Q" andQ." respectively. .The other halfzpf the network. consists of two equal coils l9 and 1 I 9" connected in series between po s R and R", avariable condenser 2il.,p ace,d;interposedbetweenrthe points S andgthe junction ofcoils I9 and I9" and theparts of .the Lecher system 3'- and 37-, located between "the points QfrRfandpQi', B" respect v y The. .caDaCif -Y- oi the. ondenser. 8;. snQWedr- Justadin such armann rc hat t e, part o h sin eeph se. circu t .etw e p nt P d: t e. pointsQ and-Q." res ec v yis t ne t the equ... of thelqqeip si l t on Sincepn y currents having the frequency of the local oscillat ons arefl wins throushthe de ser th n -ph se. ircui an h .Wncd means (of his ond n er thout com r mis n e u n t e nsh-. ul1,. rcu timilar he t of the single pl ase circuit between; points S, and Q; nd; Q, e pe t v y s l ke i un-edto heire nency it ic lo osc llations by djust: en oil-t e conden e 6-; hus. not onlythe ho e o h si eenhase irc s, n; ser e resonance with respect to the frequency; of the localoscillations butalso the antennaif, 2"'is n ec ed a a o t ee inim m of hc a 0 cill ations; so that these oscillations are not radit dion nr, pp ec b ext B a ust ent of t Le r y tem52 he .p-ushr u l ircu c n-.batun d t th r q nc f he n om scill i When making of the network set-out hereinbefore for tunin the single-phase circuit, both the junc tion of the cathode S and. the middle of the. push-"pull circuit can befgrounded. This permits't-he cathoderdi-rect current and the heating; cu-rrent to be fed directly to the point 8,

whereas inthe Circuit arrangement shown in Fig l this cantake -place only through high-frequency chokes. In this case, moreover,- the in;

ductance 22-mayberealized inthe formof acavity resonator y me s of whichtheirequency of the local oscillations can be stabilized. Tiljunction of the condensers l and '7""is preferably connectedto a tappingof this resonator.

In the arrangement shown in Fig. 1 this method.

of stabilization is not advantageous, ;since in this case. the outside of the resonator cannot be grounded with respect to high frequency.

Grounding of the point P yields the advantage that the source ofnegative grid: bias. 9% be .con-

e t d h s po w t ut .I y- Q 1D1i'Q t QI Mo ov r he: signs-la n; he: sienna halvinaa. frequency correspo ding to thomtermediate fre quencycan no longer. causecdisturbances .in the; receiverstages next tothemixing-stage. In fact,-

these signals. which are usually induced in the same :phaseon both halvesof the dipole antenna 2, 2", may cause disturbances if the push-pullavoided, however, by grounding the middle of the push-pull circuit, since in this case the impedance.

between. the antenna junctions Q2. Q and ground is very low in regard to oscillations have ing the intermediate frequency, :50 that evenw-itha. slightly asymmetrical push-pull circuit, the.

disturbances cannot. reach: to the intermediatefrequency stage. n

In some cases the condensermay be omitted;

In fact,.when tuning the part of the single-phase;

circuit which. is located between the points. Q, Q and-the points, by means of the Lecher system 3, 3', first to thefrequency of thelocal oscillations, for instance by a judicious choice of, the location of the antenna junctionsQ', Q5", and by subsequently tuning the push-pull circuit to the frequency of the incoming oscillations'the correct matching of the antenna to t-hedischarge systems-will generally be compromised. This .evil

can be; eliminated by rprovidin-gan impedance be.-.

tween points R. and-R and by-=tuning=anewithe pushpull circuit by means of v the..-.short.-circuit bridge 4 the impedance is so chosen as to achieve optimum. matchingof. the. antenna, i.. e.- a. maxi.

mum .signaleto-noise.ratioor .a maximum. ampli-.

fication. For instance, when the inductance-oi the. part of theLecher system betweenpointsQfl Q. and R, R has .becomeiihigh asia.resultof the tuning of the-saidpartof the single-phasecircuit to the frequency of thelocal oscillations,

the matching of the antenna and the-tuning-of the push-pull circuitcan be adjustBd again to their correct yaluesby-interposing a suitable in...

ductancebetween the .pointsR and R" and by tuning at the same .timethepushmull circuit by means of the'short-ci-rcuit bridgeto. the-fre quency of theincomingoscillations. If the in-- ductance of thesaid part of the Lechersystemhas become toolow; acondensershouldbesub stituted for thecoil.

Fig. 3 representssa circuit arrangement acev cording to theinvention; inwhich :the input resonant {circuit is provided between the cathodes oscillations, sothat a distinct local oscillator canbe dispensed with. Each anode circuit cornprises a coil 24, and 24"; moreover, owingto'the presenceof these -coi1s,. positive feedback is ob--- tained in regard to the incoming oscillations, as

a result of which the push-pull cirouit:isundamped.

The-.push-pull circuit consists of twc seriesconnected coils, 25': and 25 and a-tuni-ng-com denser .26.. by means of which thepush-p-ullcircuit. .can bectun-ed to-the frequencyof the incomingoscillationsr The junction]? of coils 25 and 252, which is themiddle of the push-pull circuit, is .connected directly to ground. The antenna 2-:,' 2';"2isr-inductively coupled withthe ccils 25' and 25 through an incluctanceil; On the coils 25', 25" two points Q, Q can be indicated which have the same function as the antennajunctions in the circuit shown in Figs. 1 and 2. These may be considered as points to which the antenna is effectively connected, without makingany difference in regard to the remaining part of the circuit. According to the invention a starconnection is provided between these points and the point P, the branches of the star connection being constituted by two equal coils I1 and H and a variable condenser l8.

By means of the condenser Hi the part of the single-phase circuit located between the point P and the points Q and Q" respectively can be tuned to the frequency of the local oscillations. The part of the single-phase circuit located between ground and the points Q and Q" respectively, reckoned via the point S and the points R and R is likewise tuned to the frequency of the local oscillations by making the inductance l connected between point S and ground variable and by adjusting it to the correct value. In this way the whole single-phase circuit is brought into resonance with respect to the frequency of the local oscillations, the antenna 2, 2" being at the same time connected to a voltage node of these oscillations.

By grounding the point P the cathode direct current can be supplied in a simple manner. In the present case the heating current might be fed through the intermediary of double wound coils 25', 25" to the cathodes of the triodes. When the push-pull circuit, in using ultra-short waves, is realized in the form of a Lecher-system, the heating current can be fed in a simple manner to the cathodes by making use of a Lecher system in which each conductor consists of two coaxial conductors, one of which serves in any instance for supplying and one for carrying off the heating current.

If desired, the coil [5 may be replaced by a star-connection similar to that used in the arrangement shown in Fig. 2 between points S and R. In this case two coils l9 and 19 are connected in series between the two cathodes R and R", the junction of these coils being connected through a condenser 29 to the points S. In this way also the point S may be grounded, which yields the advantage that the source of negative grid bias can be connected directly to the point S.

An an alternative, the star-connections used in Figs. 2 and 3 may be realized with two capacities and an inductance, in which the capacities are interposed between points Q and Q" and between points R and R" respectively. However, the star-connections represented in Figs. 2 and 3 permit a much simpler adjustment. the aforesaid star-connections use may also be made of the equivalent delta-connections. However, these are usually more complicated.

Fig. 4 represents a modification of the lefthand part of the push-pull circuit of the arrangement shown in Fig. 2. In this case, however, the point P is not directly grounded, but through a resistance 28.

In receivers that are tunable over a definite frequency range, it may occur that the part of the single-phase circuit between ground and the points Q and Q respectively is not exactly tuned to the frequency of the local oscillations, so that this part behaves, for instance, as a large capacity. In this case this capacity, jointly with the parallel-connected inductances of the pushpull circuit, in so far as these are located between the point P and the points Q and Q" re- Instead of spectively (in the case under view the part of the Lecher system on the left of points Q, Q) is set in parallel-resonance in regard to the said frequency, which, of course, is very undesirable. To prevent this the left-hand part of the Lecher system may be made aperiodic by connecting it to ground through a resistance 28 having a value corresponding to the surge resistance of the parallel connected Lecher lines 3, 3" with respect to ground.

' The invention applies not only to mixing circuits in which triodes are used, but also to mixing circuits in whichuse is made of diodes, tetrodes, and so on.

It is not absolutely necessary for the pair of corresponding interconnected input electrodes of the discharge systems to be directly interconnected; but sometimes it may be desirable to interconnect these electrodes, for instance, through a Lecher line or a set of coils.

What I claim is:

1. An electrical circuit arrangement for mixing a first wave and a second Wave, comprising the following elements in series circuit arrangement, first and second mixing elements arranged in parallel relationship and each comprising cooperating electrodes in capacitive relationship, means to apply said first wave in phase coincidence to said mixing elements, means including a resonant impedance system having a first point constituting a substantially electrically centered tapping to apply said second wav in push-pull relationship to said mixin elements and means to tune said series circuit to the frequency of said first wave and to provide i said impedance system second and third points at a potential node for said first wave, first and second reactive elements coupled in series between said second and third points, a third reactive element coupled between said electrically centered tapping and the junction of said first and second reactive elements to tune said first and second reactive elements to the frequency of said first wave, and means to apply said second wave to said impedance system,

2. An electrical circuit arrangement for mixing a first wave and a second wave, comprising the following elements in series circuit arrangement, first and second mixing elements arranged in parallel relationship and each comprising cooperating electrodes in capacitive relationship, means to apply said first wave in phase coincidence to said mixing elements, means including a resonant impedance system toned to the frequency of said second wave and having a first point constituting a substantially electrically centered tapping to apply said second wave in push-pull relationship to said mixing elements and means to tune said series circuit to the frequency of said first wave and to provide in said impedance system second and third points at a potential node for said first wave, first and second reactive elements coupled in series between said second and third points, a third reactive element coupled between said electrically centered tapping and the junction of said first and second reactive elements to tune said first and second reactive elements to the frequency of said first wave, and means to apply said second wave to said impedance system at said points of voltage node of said first wave.

3. An electrical circuit arrangement for mixing a first wave and a second wave, comprising the following elements in series circuit arrangement, first and second mixing elements arranged in' parallel relationship and each comprising-cooperating 1 electrodes in capacitive relationship,

means to apply said first wave in phase coincidence to saidmixing elements, a Lecher system comprising first and second conductors'havingan junction of said first and second reactive ele-.

ments to tune said, first and second reactive elements to'the frequency of said first wave, and means to apply said second wave to said Lechersystem-at said points of potential node.

4 An electrical circuit arrangement for mixing a first wave'and a second wave, comprising a pair of mixing elements each having cathode, grid and anode electrodes, said electrodes having interelectrode capacities therebetween, a Lecher system comprisingfirstand second conductors having an open end thereof coupled to said grids in push-pull relationship and having a closed end to tune said Lecher system to the frequency of-said second wave, means to interconnect said cathodes, an inductive element coupled in regenerative relationship between said cathodes and said anodes to apply said first wave tosaid cathodes in phase coincidence, a first impedance network intercoupling said control grids and said cathodes and having a variable reactive element to produce on each of said conductors a potential node for said firstwave at points intermediate to said closed end and said grids, a second impedance network intercoupling said points of potential node and said closed end and having a second variable reactive element to tune said second impedance network to the frequency of said first Wave, said Lecher system, said first impedance network and said second impedance network constituting a series circuit tuned to the frequency of said first wave, and means to apply said second Wave to said Lecher-system at said points of potential node.

5. An electrical circuit arrangement for mixing a first wave and a second Wave, comprising a pair of mixing elements each having cathode, grid and anode electrodes, said electrodes having interelectrode capacities therebetween, a Lecher system comprising first and second conductors having an open end thereof coupled to said grids in push-pull relationship and having a closed end to tune said Lecher system to the frequency of said secondlwave, means to interconnect said cathodes, a first inductive element coupled in regenerative relationship between said cathodes and said anodes to apply said first Wave to said cathodes in phase coincidence, an impedance network including said grid-cathode interelectrode capacities intercoupling said control grids and said cathodes and having a variable capacitive element to produce on each of said conductors a potential node for said first wave at points intermediate to said closed end and said grids, second and third inductive elements coupled in series between said points of potential node, a second variable capacitive element coupled between the junction of said second and third inductive elem'ents and'said closedend'to tune said second and third: inductive elements to the fre-. quency'of said firstswa've, said Lecher. system, said impedance network; said secondand'th'ird inductive elements and" said second 'va'riable capacitive element constituting two series'circuits tuned to the frequencyliof said first wave, and means to apply said seco'nd wave to said Lechersystem at said points of "potential node.

6. An electrical circuit arrangementformixing a first wave andta second wave'; comprising a pair of mixing elements" each having cathode, grid andanode ele'ctrodes,'said electrodes-"having interelectrode 'capaciti'estherebetween, an riput network tuned T to "the frequency "of said second wave and coupled to said 'cathodes in push pull relationship; said input networkincluding an-inductor having three taps, one of; said tapsecnstituting a substantially electrically' centered tapping of said input network,means -to couple said centered tapping to ground potential,- means to interconnect said grids, -a'firs'l',"reactive'- element coupled between said grids and-ground potential, said. first reactive element,- said I cathode interelectrode capacities and said input network constituting a pair of series circuits-each tuned to the frequency of said first wave,

ond reactive element coupled in regenerative relationship between said grids and said anodes to apply said first 'wave -to said-grids in-plia'se coincidence, means to produce potential nodes for the frequency ofsaid first wave' at-the-- other taps ofsaid-inductor comprising an impedance network tuned to the frequency of said first wave and intercoupling the taps on said inductor, and means to apply said second wave to said inductor.

'7. An electrical circuit arrangement for mixing a first wave and a second wave, comprising a pair of mixing elements each having cathode, grid and anode electrodes, said electrodes having interelectrode capacities therebetween, an input network tuned to the frequency of said second wave and coupled to said cathodes in push-pull relationship, said input network including an inductor having three taps, one of said taps constituting a substantially electrically centered tapping of said input network, means to couple said centered tapping to ground potential, means to interconnect said grids, a first inductive element coupled between said grids and ground potential, said first reactive element, said gridcathode interelectrode capacities and said input network constituting a pair of series circuits each tuned to the frequency of said first wave, a second inductive element coupled in regenerative relationship between said grids and said anodes to apply said first wave to said grids in phase coincidence, means to produce potential nodes for the frequency of said first wave at the other taps of said inductor comprising third and fourth inductive elements coupled in series between the other taps of said inductor, a variable capacitive element coupled between the junction of said third and fourth inductive elements and said centered tapping to tune said third and fourth inductive elements to the frequency of said first wave, and means to apply said second wave to said inductor.

8. An electrical circuit arrangement for mixing a first wave and a second wave, comprising the following elements in series circuit arrangement, first and second mixing elements arranged in parallel relationship and each comprising cooperating electrodes in capacitive relationship, means to apply said. first wave in phase coincidence to said mixing elements, means including a resonant impedance system having a first point constituting a substantially electrically centered tapping to apply said second wave in push-pull relationship to said mixing element, a resistive element coupled between said tapping and ground potential and means to tune said series circuit to the frequency of said first wave and to provide in said impedance system second and third points at a potential node for said first wave, first and second reactive elements coupled in series between said second and third points,

'a third reactive element coupled through said resistance element between said electrical center and the junction of said first and second reactive elements to tune said first and second reactive elements to the frequency of said first wave, and means to apply said'second wave to said impedance system.

9. An electrical circuit arrangement for mixing a first wave and a second wave, comprising the following elements in series circuit arrangement, first and second mixing elements arranged in parallel relationship and each comprising cooperating electrodes in capacitive relationship, means to apply said first wave in phase coincidence to said mixing elements, a Lecher system comprising first and second conductors having an open end thereof coupled to said mixing elements in push-pull relationship and having a closed end to tune said Lecher system to the frequency of said second wave, a resistive element coupled between ground potential and said closed 12 end and means to tune said series circuit to the frequency of said first wave, and to produce on each of said conductors a potential node for said first wave at points on said conductors intermediate to said closed end and said mixing elements, first and second reactive elements coupled in series between said points on said conductors, a third reactive element coupled between ground potential and the junction of said first and second reactive elements to tune said first and second reactive elements to the frequency of said first wave, and means to apply said first wave to said Lecher-system at said points of potential node.

ADELBERT VAN WEEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Fyler Aug. 16. 1949 

